A wire-cutting electroerosion machine makes use of a continuous wire electrode composed of a metal such as copper or tungsten or an alloy such as brass and having a thickness generally ranging between 0.05 and 0.5 mm .phi.. The wire electrode is axially displaced by a drive means and thereby advanced and transported from a supply side to a collection or takeup side through a cutting zone in the region of a workpiece at a rate of axial displacement of, say 1 to 2 m/min. For defining the cutting zone a pair of guide members may be arranged to provide a straight line path along which the wire electrode is passed and juxtaposed in a machining relationship with the workpiece across a minute machining gap. A machining liquid, e.g. a liquid dielectric such as distilled water or a liquid electrolyte, is supplied to fill and flush the machining gap while an electric current is applied between the wire electrode and the workpiece to produce a succession of electrical discharges and/or an intense electrolytic action through the fluid medium, thereby permitting material to be electroerosively removed from the workpiece. As material removal proceeds, the workpiece is displaced relative to the axially traveling electrode and generally transverse to the axis thereof along a prescribed path to form a desired cut in the workpiece.
In the path of wire travel, the drive means is typically constituted by drive rollers driven by a motor and provided immediately upstream of the collection or takeup side to apply a traction force to the wire. Brake rollers driven by a motor may further be provided immediately downstream of the supply side to assure that the wire travels stretched under a suitable tension and at a desired rate of advance along the path and through the cutting zone defined between the machining guide members. Additionally and depending on the locations of the wire supply and collection sites, further wire guides may be provided in the path of the traveling wire to change the direction of wire travel from the supply side to the cutting zone and from the latter to the collection side, respectively.
Heretofore, various forms of each of the machining guide members have been in use. One makes use of a die or an internal passage formed through an elongated solid member. This structure is, however, inconvenient for mounting and dismounting the continuous wire. In another form, a V-shaped notch formed on a fixed guide body provides a bearing surface for the traveling wire but this tends to cause the traveling wire to come off, thereby giving rise to machining inaccuracy.
Means for conducting the machining current to the traveling wire-electrode has hitherto been available basically in two forms.
In a first form, an electrically conductive block with a terminal element leading via a cable to a source of the machining current has a pin or projection formed with a recess located in the path of wire travel. The block is securely mounted on a portion of the electroerosion machine and the wire electrode is guided to pass through the recess of the pin in a frictional contact therewith. Due to the minor interfacial surface irregularities, the moving wire tends to be scratched on the open guide recess and consequently tends to be locally floated, tumbled or jumped, causing the wire to be irregularly vibrated due to the resulting tension fluctuation. As a result, an undesirable wavy formation or longitudinal scar tends to develop on the machined workpiece surface, a cause of deterioration of the surface finish and machining accuracy. Further, undesirable electrical discharges are created between the surface of the tumbling wire and the pin recess, leaving discharge flaws on the guide surface which facilitate the scratching and the development of abnormal discharges and may also result in breakage of the wire electrode.
In a second form, a conducting wheel is rotatably supported via ball bearings on a conducting block having a terminal element leading via a cable to a source of the machining current and has a peripheral recess located in the path of wire travel. The block is here again securely mounted on a portion of the electroerosion machine and the wire electrode is guided to pass through the recess. In this arrangement, the undesirable development of abnormal electrical discharges at the ballbearing portions between the conducting block and the wheel is further added, tending to damage the ball bearings and hence to arrest smooth rotation of the conducting wheel and to limit the life of the conductor assembly.